Yes, most hydraulic cylinders can be rebuilt. It's not a difficult task to do if you're mechanically inclined, though you may need some special wrenches to disassemble it. Grab your phone book and look up a hydraulic shop- if you cant find one, try a construction equipment dealer or forklift dealership. The toughest part may be finding a seal kit for it. The hydraulic shop should be able to cross reference the numbers on it to get the proper seals, or it may have to be disassembled and measured. I'd try that first. Construction equipment, forklift, and even farm equipment dealerships should have pretty good access to hydraulic components, however they may not be able to cross reference any part numbers that may be on the cylinder, or order seals by their actual size.
The cylinder itself is pretty basic. If you look at the end the rod comes out of, there should be some holes or slight notches drilled or machined in the cylinder housing. These are designed for a special gland nut wrench to fit into and the end of the cylinder will actually unscrew. If you dont have the correct wrench, you may be able to get it loose with a big pair of channel locks, a strap/ chain wrench, or by putting a punch in one of the gland wrench holes/ slots and driving it around with a hammer. Once the nut comes loose, look inside the cylinder with a flashlight. There may be some snap rings in there that hold a packing seal in place. If thee are, remove them. Then the rod should slide out of the cylinder body.
There will be a seal assembly inside the gland nut called a 'wiper seal' or something of that nature. You will need to replace that, because that seal is what keeps dirt/ dust/ wood slivers that land on the rod from entering the cylinder ad damaging other seals. There will also be a secondary packing either on the inside edge of the nut, if you didnt remove a snap ring inside the cylinder. That seal makes it possible for fluid to build pressure and return the rod inside the cylinder.
On the end of the rod that's in the cylinder, there will be a large end with a set of seals on it. All those seals need to be replaced, as they are what failed to cause it to leak internally.
Once you go inside, it's a good idea to just replace all the seals you disturb. They're relatively cheap, compared to having to remove the cylinder from the splitter again and do it over. Also, have a drain bucket and lots of rags. No matter if the cylinder is extended or retracted, it's full of fluid. A lot of it should drain out when you remove the lines, but there will still be some trapped inside that will come out when you remove the gland nut.
Be very, very careful not to nick, ding, scratch, or otherwise damage the surface of the rod or the inside of the cylinder. Rough spots on either will destroy seals in a hurry. As you remove the rod, insect it very, very carefully for existing damage. If you find any, the cylinder assembly may need to be replaced. Be sure to wrap the rod in shop rags when you lay it on the workbench, or cover the bench with a towel. As you tear into it, you'll find it's a really simple design- basically just swap your old seals for new ones, and reassemble in the exact opposite order from how it came apart.
Nothing else jumps out at me right now, but I'll keep an eye on this thread. I've rebuilt more cylinders than I care to count.
